54 THE SENSES OF ANIMALS 



made later. Once the snake has come up on its prey the eyes 

 will take over, and provided that the victim is not beyond 

 the striking distance of the particular snake in question the 

 aim will usually be sure and capture certain. 



It is perhaps worth referring here to the encounters be- 

 tween snakes and mongooses, since these show how the 

 snake's sight can in such cases lead to error which would not 

 occur when the snake is pursuing prey such as rodents, 

 lizards, frogs and so on. 



Being short-sighted, the snake is at a disadvantage when 

 encountering a mongoose, for the mongoose's defence is its 

 great agility coupled with the fact that it can, by muscular 

 action of the skin, cause its fur to stand out all over its body, 

 thus making it appear bigger than it really is. The snake 

 keeps striking at the swiftly moving outline of the mongoose's 

 body but fails to get home, more often than not, being unable 

 to detect the actual body of its opponent and "striking short" 

 in consequence. The mongoose keeps darting at the snake 

 and then, by reason of its quickness, jumping back to avoid 

 the attack of the snake. This goes on until the snake is 

 literally tired out, when the mongoose will dash in and bite 

 the snake — usually just behind the head. 



Returning to the question of what part the eyes play in 

 capturing food, it is clear that many species of snake, once 

 having located their prey, will quickly detect any kind of 

 movement, and will then seize it ; the last part of this move- 

 ment or series of movements is visual in origin. At fairly 

 close quarters the eyesight is keen and even the pulsating skin 

 under a frog's lower jaw is quite enough to stimulate a snake 

 to strike. The actual strike is very quick indeed ; it has to be, 

 since many of the animals eaten by snakes — voles and mice 

 and rats for instance — are themselves very quick in their 

 movements ; and though at the first sight of an attacking 

 snake a rodent will "freeze" and remain still as if hypnotized, 

 any delay in attacking may cause the rodent to scuttle away. 

 The snake, therefore, must strike instantly if it is not going 

 to miss. This particularly applies to those snakes which, in 

 feeding, merely swallow their prey whole; if the prey is 

 missed at the first attempt the snake may not get another 

 chance. On the other hand, venomous snakes, such as our 



